This invention relates to AC machines, and particularly to such machines utilizing armature conductors mounted in the air gap on supports attached to the stator core.
In certain large AC machines, such as those having superconducting field coils, insulated armature conductor bars are mounted in the air gap between the stator and the rotor. A design requirement for such machines is a rigid attachment in the radial and azimuthal directions. The rigid attachment is necessary, in order for the connections between the conductor bars and the stator core to withstand the short circuit forces applied to the conductor bars when a sudden surge in armature current occurs, and to limit vibratory motion of the conductor bars under the influence of running forces.
In operation, an axially-long electrodynamic machine develops a heat concentration in the armature conductor bars due to the current passage therethrough. The iron stator core has a coefficient of thermal expansion different from that of the armature conductor bars normally made of copper. As a result, the conductor bars experience a different axial expansion from that experienced by the stator core. Therefore, an arrangement is required which provides a flexible connection in the axial direction between the armature conductor bars and the stator core.
A means of mounting armature conductors to a stator of an AC machine is disclosed in U.S. Pat. No. 3,405,297, to Madsen, issued Oct. 8, 1968. In that patent is disclosed a means of affixing armature conductors to the stator core by an axial wedge-shaped tooth which holds the insulated conductors by compression to the stator core. This provides the necessary rigid connection in two directions, but can accommodate axial thermal expansion only by slippage between the tooth and the conductors.
Another known technique for attaching armature conductors to a stator core is disclosed in U.S. Pat. No. 3,082,337, issued Mar. 19, 1963 to Horsley. In that patent is disclosed a method of embedding armature conductors in an insulating material in the air gap. The insulating material is cast molded with the conductors located in the casting. Again, the connection between the conductors and the supporting means is rigid in all directions. Differential thermal expansion, therefore, results in substantial stress at the interface between the conductors and the insulating supports.
In prior art techniques of attaching the armature conductors to stator core, the conductors were fitted into slots in mounting teeth and secured by mechanical means, such as wedges, or by adhesives. Mounting teeth were rigidly secured to the stator iron core, e.g., by adhesives. With either wedge or adhesive mounting of the armature conductors, the thermal expansion of the armature conductors due to heating by the armature current had to be accommodated by a relative slippage between the conductors and the mounting teeth. Resultant relative movement between armature conductors and the mounting teeth produced abrasion on the insulating material coating the armature conductors. This abrasion clearly was undesirable.
Armature conductor bars in AC machines are surrounded by an insulating layer having a limited mechanical capability to tolerate shear stress. When a conductor expands, a rigid axial mounting would cause all the stress created by the thermal expansion to be applied to the insulating material. The limited stress capabilities of the insulation require that some means be provided to allow for differential expansion between a stator iron core and the armature conductors, in elements other than the insulation.
The object of the present invention is to provide a mounting structure for armature conductors in AC machines which will provide rigid attachment in the radial and azimuthal directions, and also limit the axial shear load on the armature conductor insulation, due to relative motion caused by differential thermal expansion between the armature conductors and the stator iron core, to a level within the mechanical stress tolerance capabilities of the insulation material.